Having these implementation available crate-wide means that platforms not using sockets for their networking code have to stub out the libc definitions required to support them. This PR moves the conversions to private helper functions that are only available where actually needed.
I also fixed the signature of the function converting from a C socket address to a Rust one: taking a reference to a `sockaddr_storage` resulted in unsound usage inside `LookupHost::next`, which could create a reference to a structure smaller than `sockaddr_storage`. Thus I've replaced the argument type with a pointer and made the function `unsafe`.
`IN6ADDR_ANY_INIT` and `IN6ADDR_LOOPBACK_INIT` documentation.
Added documentation for IPv6 Addresses `IN6ADDR_ANY_INIT` also known as `in6addr_any` and `IN6ADDR_LOOPBACK_INIT` also known as `in6addr_loopback` similar to `INADDR_ANY` for IPv4 Addresses.
Added documentation for IPv6 Addresses `IN6ADDR_ANY_INIT` also known as
`in6addr_any` and `IN6ADDR_LOOPBACK_INIT` also known as
`in6addr_loopback` similar to `INADDR_ANY` for IPv4 Addresses.
